Supersonic treatment of vapor streams for separation and drying of hydrocarbon gases

ABSTRACT

Selective recovery of C2 to C4 hydrocarbons is achieved through the use of a converging-diverging nozzle, or de Laval nozzle. The vapor stream comprising C2 to C4 hydrocarbons is fed into an inlet of a de Laval nozzle having a throat. The vapor stream may have an initial temperature of between 0° C. and 100° C., and an initial pressure of between 200 psig and 500 psig. In the de Laval nozzle, the vapor stream expands after passing through the throat of the de Laval nozzle, producing a vapor stream having re-duced temperature and pressure. Then, C2 to C4 hydrocarbons condense from the reduced-temperature vapor stream as liquid droplets, which may be recovered. Fractionation of C2 to C4 hydrocarbons by means of a de Laval nozzle is possible; the technique allows select-ive recovery of propane from a mixture of propane and ethane.

BACKGROUND Field of the Invention

This disclosure relates generally to:

-   -   drying volatile hydrocarbon gases by condensation, and to        recovering and/or recycling dried hydrocarbon gases; and to:    -   recovering and/or recycling reactive hydrocarbon gases by        condensation.

Description of Related Art

A de Laval nozzle, or convergent-divergent nozzle, is a tube that ispinched in the middle, and has an axisymmetric hourglass shape. De Lavalnozzles are used to accelerate pressurized gases at low speed to ahigher speed, more particularly a supersonic speed in the axialdirection, by converting the heat energy of the flow into kineticenergy. Because of this, the nozzle is used in steam turbines, rocketengine nozzles, and supersonic jet engines.

Operation of a de Laval nozzle depends on changing properties in a gasas it accelerates from subsonic to supersonic speeds. The speed of asubsonic flow of gas will increase if the pipe carrying it narrowsbecause the mass flow rate is constant. The gas flow through a de Lavalnozzle is normally isentropic. At the “throat,” where thecross-sectional area is at its minimum and flow is choked, the gasvelocity reaches Mach 1. As the nozzle cross-sectional area increases,the gas expands, and the gas velocity becomes supersonic. Underconditions of supersonic flow at constant, or nearly constant, entropy,the gas temperature decreases and the gas pressure decreases.

As the gas temperature decreases, gases within the stream may condenseand form a liquid or solid phase. By inducing swirl in the gas flow, thecondensed phase may be driven by centrifugal force to the wall of thenozzle, and recovered through an opening at the nozzle wall or in a flowpipe leading away from the nozzle. Such techniques have been used toremove water from methane streams, e.g., natural gas. The currentapplication is directed to removing water from higher-boilinghydrocarbon streams, and/or effectively separating C2 to C4 hydrocarbonsunder supersonic conditions.

Such separations are illustrative of those that can be achieved by thevarious embodiments disclosed herein, and are not intended to beexhaustive or limiting of the possible advantages that can be realized.Thus, these and other embodiments will be apparent from the descriptionherein or can be learned from practicing the various exemplaryembodiments, both as embodied herein or as modified in view of anyvariation that may be apparent to those skilled in the art. Accordingly,the present invention is exemplified by, but not limited to, themethods, arrangements, combinations, and improvements herein shown anddescribed.

SUMMARY OF THE DISCLOSURE

In light of the present need for improved methods of recovering and/orrecycling volatile hydrocarbon gases, a brief summary of variousembodiments is presented. Some simplifications and omissions may be madein the following summary, which is intended to highlight and introducesome aspects of the various exemplary embodiments, but not to limit thescope of the invention. Detailed descriptions of a preferred exemplaryembodiment adequate to allow those of ordinary skill in the art to makeand use the inventive concepts will follow in later sections.

Supersonic separation methods operate by accelerating a gas mixture tosupersonic speeds by passing the mixture through a converging-divergingnozzle. The expansion process lowers the temperature and pressure of thegas mixture. If the partial pressure of a condensable component in thevapor is decreased below the vapor pressure of that component at thelocal temperature, homogeneous nucleation can commence, initiating theformation of small droplets of the condensate that may then grow viacondensation and coagulation mechanisms. These droplets are typicallyvery small (of the order of 0.1 microns) and generally travel with thespeed of the gas. To collect these droplets, supersonic separatorsutilize swirl vanes and other devices to induce centripetal accelerationof the droplets toward the nozzle walls, where they may be captured. Theswirling devices also increase local turbulence levels within theseparator, greatly increasing the probability of droplet-dropletcollisions which lead to larger droplet volumes and enhanced potentialfor collection.

In various embodiments disclosed herein, a stream of gases or a mixtureof gas and vapor passes through a de Laval nozzle. At the throat of thede Laval nozzle, the gas velocity reaches sonic velocity, i.e., thevelocity c=Mach 1. Prior to entering the throat, gas velocity c issubsonic, while after exiting the throat, gas velocity c is supersonic.As the gas leaves the nozzle at supersonic speed, both pressure andtemperature fall.

Various embodiments of the disclosed process are used for gasseparation. In particular, the process is directed towards condensing C3and/or C4 hydrocarbons and other heavy components from a gas streamcomprising C1 to C4 hydrocarbons, methane, oxygenated compounds(propanols, butyraldehydes, etc.), and various inorganic gases using aLaval nozzle.

Various embodiments of the disclosed process are used for drying ofhydrocarbon gases. In particular, the process is directed towardscondensing water from a vapor stream containing C1 to C4 hydrocarbons,water vapor, and various inorganic gases using a Laval nozzle to producea dry vapor stream.

In embodiments directed to gas separation or drying, a stream of gasesor a mixture of gas and vapor passes through a de Laval nozzle, andaccelerates to supersonic speed (c>Mach 1). As the gas leaves the nozzleat supersonic speed, both pressure and temperature fall. Gases derivedfrom higher boiling materials condense as a liquid, and low-boilinggases are recovered as gases. The stream of gases is subjected to avortex chamber or similar device, which causes vapors to swirl around acentral axis as they leave the nozzle; centrifugal forces aid inseparation of condensed gases from the gas or vapor stream.

Various embodiments relate to treatment of C3 hydrocarbons, includingpropene (propylene) gas, from a purge stream from a hydroformylationreaction process, where propene gas reacts with hydrogen and carbonmonoxide to produce butyraldehydes.

Various embodiments disclosed herein are directed to a method ofselectively recovering hydrocarbons with a boiling point of between−105° C. and 5° C. from a vapor stream. In some embodiments, the vaporstream may contain, based on the total weight of the hydrocarbon gases:

-   -   from 50% to 100% C3 hydrocarbons, from 70 to 100% C3        hydrocarbons, from 85 to 100% C3 hydrocarbons, or from 85% to        98% C3 hydrocarbons; and from 0% to 10% methane, from 0.5% to 5%        methane; or from 1% to 3% methane;    -   with the balance being C2 and C4 hydrocarbons.

In some embodiments, the vapor stream may contain, based on the totalweight of the hydrocarbon gases:

-   -   from 50% to 100% C4 hydrocarbons, from 70 to 100% C4        hydrocarbons, from 85 to 100% C4 hydrocarbons, or from 85% to        98% C4 hydrocarbons; and    -   from 0% to 10% methane, from 0.5% to 5% methane; or from 1% to        3% methane;    -   with the balance being C2 and C3 hydrocarbons.

In some embodiments, the vapor stream may contain greater than 50%,greater than 70%, or greater than 85% C2 hydrocarbons; and less than10%, less than 50%, or less than 3% methane, with the balance being C3and C4 hydrocarbons.

In various embodiments, the method comprises passing a vapor streamcomprising hydrocarbons with a boiling point of between −105° C. and 5°C. into an inlet of a de Laval nozzle having a throat, said vapor streamhaving an initial temperature of between 0° C. and 100° C. and aninitial pressure of between 200 psig and 500 psig; an initialtemperature of between 0° C. and 60° C. and an initial pressure ofbetween 250 psig and 400 psig; or an initial temperature of between 0°C. and 40° C. and an initial pressure of between 275 psig and 325 psig;expanding the vapor stream after the vapor stream passes through thethroat of the de Laval nozzle, producing a reduced-temperature vaporstream;

-   -   condensing hydrocarbons with a boiling point of between −105° C.        and 5° C. from the reduced-temperature vapor stream as liquid        droplets; and    -   recovering the liquid droplets of condensed hydrocarbons from        the vapor stream.

In various embodiments, the liquid droplets have a mean diameter ofbetween 1.75×10⁻⁵ m and 2.5×10⁻⁶ m.

In various embodiments, there is a step of inducing swirling flow in thevapor stream, either prior to expanding the vapor stream, or afterexpansion, but before recovering the liquid droplets. During therecovery step, the swirling flow drives the liquid droplets toward thewall of the de Laval nozzle, or toward the wall of a pipe connected toan exit of said de Laval nozzle, by centrifugal force.

In various embodiments, the initial vapor stream comprises hydrocarbonswith a boiling point of between −40° C. and −60° C., i.e., propane,propene, and mixtures thereof, in an amount of between 85% and 100% byweight of the hydrocarbon gases. In other embodiments, the initial vaporstream comprises hydrocarbons with a boiling point of between −20° C.and 5° C., i.e., saturated C4 hydrocarbons, unsaturated C4 hydrocarbons,and mixtures thereof; in an amount of between 70% and 100% by weight ofthe hydrocarbon gases. In some embodiments, the initial vapor streamcomprises hydrocarbons with a boiling point of between −105° C. and −85°C., i.e., ethane, ethane (ethylene), and mixtures thereof, in an amountof between 50% and 100% by weight of the hydrocarbon gases.

In addition to hydrocarbon gases, the vapor stream may comprisehydrogen, carbon monoxide, carbon dioxide, and various inert inorganicgases. In various embodiments, the vapor stream may comprise oxygenatedorganic compounds. For example, the vapor stream may be a waste gas froma hydroformylation reactor where propene is converted intobutyraldehyde. In such a case, the waste gas stream would comprise bothunreacted propene and C4 aldehyde products. In a case where C3hydrocarbons, for example, comprise between 85% and 100% by weight ofthe hydrocarbon gases, they may only comprise between 22% and 78% byweight of the total vapor stream, including inert gases and oxygenatedcompounds.

Various embodiments disclosed herein relate to a method of recovering C2to C4 hydrocarbons in a waste gas stream from a chemical reactor, bypassing the waste gas stream into an inlet of a de Laval nozzle having athroat, where the waste gas stream has an initial temperature of between0° C. and 100° C., between 0° C. and 60° C., or between 0° C. and 40°C., and an initial pressure of between 200 psig and 500 psig, between250 psig and 400 psig, or between 275 psig and 325 psig;

-   -   expanding the waste gas stream after the vapor stream passes        through the throat of the de Laval nozzle, producing a        reduced-temperature stream;    -   condensing C2 to C4 hydrocarbons from the reduced-temperature        stream as liquid droplets; and    -   recovering the liquid droplets of condensed C2 to C4 hydrocarbon        gases from said reduced-temperature stream.

The C2 to C4 hydrocarbons may be saturated hydrocarbons, unsaturatedhydrocarbons, or a mixture thereof. At least a portion of the recoveredC2 to C4 hydrocarbons may be fed to the chemical reactor as a reactant.

In various embodiments, the C2 to C4 hydrocarbons comprise C2 to C4unsaturated hydrocarbons, and are recovered from a waste gas stream froma hydroformylation reactor. If the waste gas stream is derived from ahydroformylation reactor, the waste gas stream may comprise C3 to C5oxygenated compounds, particularly aldehydes, in addition to C2 to C4hydrocarbon gases. In such a case, the method may further comprise astep of condensing the oxygenated compounds from said waste gas streamprior to passing the waste gas stream into the inlet of the de Lavalnozzle so as to prevent contamination of the condensed hydrocarbon gasesby the oxygenated compounds. Alternatively, a waste gas streamcomprising C2 to C4 hydrocarbon gases and vapor-phase C3 to C5oxygenated compounds may be treated by expansion in a de Laval nozzle tocondense droplets comprising hydrocarbons and C3 to C5 oxygenatedcompounds. The resulting condensed mixture may be distilled to recovervolatile hydrocarbons as an overhead stream.

In various embodiments, the C2 to C4 hydrocarbons are recovered from awaste gas stream from a gas phase polymerization reactor, and compriseC2 to C4 unsaturated reactant hydrocarbons, e.g., ethene, propene,and/or butenes. The waste gas stream may additionally comprise lowmolecular weight oligomers having a boiling point of between 5° C. and100° C., e.g., dimers, trimers, and/or tetramers. If the waste gasstream comprises C2 to C4 reactant hydrocarbons and oligomers, themethod of recovering C2 to C4 hydrocarbons may further comprise a stepof condensing hydrocarbons having a boiling point of between 5° C. and100° C. from the waste gas stream prior to passing the waste gas streaminto the inlet of the de Laval nozzle.

In various embodiments, the initial vapor stream comprises hydrocarbons,i.e., propane, propene, and mixtures thereof, in an amount of between85% and 100% by weight of the hydrocarbon gases. In other embodiments,the initial vapor stream comprises hydrocarbons, i.e., saturated C4hydrocarbons, unsaturated C4 hydrocarbons, and mixtures thereof in anamount of between 70% and 100% by weight of the hydrocarbon gases. Insome embodiments, the initial vapor stream comprises hydrocarbons, i.e.,ethane, ethene, and mixtures thereof in an amount of between 50% and100% by weight of the hydrocarbon gases.

The recovered liquid C2 to C4 hydrocarbons may be fractionated bydistillation to produce a first fraction of C2 hydrocarbons with aboiling point of between −105° C. and −85° C.; a second fraction of C3hydrocarbons with a boiling point of between −40° C. and −60° C.; and athird fraction of C4 hydrocarbons with a boiling point of between −20°C. and 5° C. Where the waste gas is derived from a chemical reactor forproduction of butyraldehyde by hydroformylation or for production ofpolypropene, at least a portion of second fraction of C3 hydrocarbonsmay be recycled to the chemical hydroformylation reactor as a reactant.The C2 and C4 fractions may be fed to a cracking plant or anincinerator.

Alternatively, the C3 fraction boiling between −40° C. and −60° C. mayundergo further fractionation to produce a propane-rich fraction and apropene-rich fraction. This may be done by selective adsorption ofpropene onto a zeolite molecular sieve, by distillation, or withselectively permeable polyimide or cellulosic membranes. If the initialfeed stream contains from 85% to 100% C3 hydrocarbon gases based on thetotal weight of the hydrocarbon gases, fractionation of gases condensedin the de Laval nozzle into a propane-rich fraction and a propene-richfraction may be performed without requiring an initial fractionationinto a first fraction of C2 hydrocarbons; a second fraction of C3hydrocarbons; and a third fraction of C4 hydrocarbons. The propene-richfraction may be used as a reactant feed stream in a chemical reactor,such as a hydroformylation reactor or a gas phase polymerizationreactor. The propane-rich fraction may be used as a feed stream for acracking plant or an incinerator.

If the initial vapor stream is a waste gas from a chemical reactionusing propene as a starting material, e.g., hydroformylation of propeneto produce butyraldehyde or gas-phase propene polymerization, thepropene-rich fraction may be recycled to the reaction vessel as astarting material.

Various embodiments disclosed herein relate to a method of recycling C3hydrocarbons in a waste gas stream from a chemical reactor, e.g., ahydroformylation or polymerization reactor. The method involves passinga waste gas stream comprising C3 hydrocarbons into an inlet of a deLaval nozzle having a throat, said waste gas stream having an initialtemperature of between 0° C. and 100° C. and an initial pressure ofbetween 200 psig and 500 psig;

-   -   expanding the waste gas stream after the vapor stream passes        through the throat of the de Laval nozzle, producing a        reduced-temperature stream;    -   condensing a first portion of the C3 hydrocarbons from the        reduced-temperature stream as a liquid, wherein about 12% by        weight and about 40% by weight of the C3 hydrocarbons in the        initial feed stream are condensed from the reduced-temperature        stream as a liquid;    -   allowing non-condensed gases to exit the de Laval nozzle; and        recovering the first portion from said reduced-temperature        stream.

In some embodiments, the method further comprises passing saidnon-condensed gases into an inlet of a second de Laval nozzle having athroat, said non-condensed gases having an initial temperature ofbetween 0° C. and 100° C. and an initial pressure of between 200 psigand 500 psig;

-   -   expanding the non-condensed gases in the second de Laval nozzle;    -   condensing a second portion of said C3 hydrocarbons from the        expanded non-condensed gases as a liquid, wherein between about        12% by weight and about 40% by weight of said C3 hydrocarbons in        the non-condensed gases are condensed as the second portion; and    -   recovering the second portion of said liquid C3 hydrocarbons.        Non-condensed gases exiting an outlet of the second de Laval        nozzle may comprise further C3 hydrocarbons, and may be passed        to at least a third de Laval nozzle for further C3 hydrocarbon        recovery, if desired. Hydrocarbon recovery may thus be        accomplished by passing a gas with condensable hydrocarbon        gases, e.g., C2 to C4 gases, preferably C3 gases, through two de        Laval nozzles in sequence, through three de Laval nozzles in        sequence, or through four or more de Laval nozzles in sequence.

In various embodiments, the method further comprises:

-   -   feeding at least a part of the first portion to the chemical        reactor as a reactant;    -   feeding at least a part of the second portion to the chemical        reactor as a reactant; or    -   mixing the first portion and the second portion to make a        mixture, and feeding at least a part of the mixture to the        chemical reactor as a reactant.

In various embodiments, the method further comprises:

-   -   fractionating the first portion into a propane-rich fraction and        a propene-rich fraction; and    -   feeding at least a part of the propene-rich fraction to the        chemical reactor as a reactant; or    -   mixing the first portion and the second portion to make a        mixture, fractionating the mixture into a propane-rich fraction        and a propene-rich fraction; and    -   feeding the propene-rich fraction of the mixture to the chemical        reactor as a reactant.

Various embodiments disclosed herein relate to methods of drying a vaporstream comprising C1 to C4 hydrocarbon gases, by passing said vaporstream comprising said C1 to C4 hydrocarbon gases into an inlet of a deLaval nozzle having a throat, the vapor stream having an initialtemperature of between 25° C. and 90° C., between 25° C. and 60° C., orbetween 25° C. and 40° C. and an initial pressure of between 150 psigand 1000 psig, wherein the vapor stream contains 500 to 10,000 ppm H₂Oby volume;

-   -   expanding the vapor stream after the vapor stream passes through        the throat of the de Laval nozzle, producing a        reduced-temperature vapor stream;    -   condensing said H₂O from the reduced-temperature vapor stream to        produce a dried stream; and    -   recovering the condensed H₂O from said vapor stream;    -   wherein the dried stream comprises C1 to C4 hydrocarbon gases        and from 0 ppm to 150 ppm water.

Various embodiments disclosed herein relate to methods of reducing themoisture content of a vapor stream comprising C1 to C4 hydrocarbon gasesand at least 500 ppm H₂O, by passing the vapor stream into an inlet of ade Laval nozzle having a throat, said vapor stream having an initialtemperature of between 25° C. and 90° C., between 25° C. and 60° C., orbetween 25° C. and 40° C. and an initial pressure of between 150 psigand 1000 psig;

-   -   expanding the vapor stream after the vapor stream passes through        the throat of the de Laval nozzle, producing a        reduced-temperature vapor stream;    -   condensing said H₂O from the reduced-temperature vapor stream to        produce a dried stream;    -   recovering the condensed H₂O from said vapor stream;    -   wherein the partial pressure of H₂O in the vapor stream is up to        the vapor pressure of H₂O at the initial temperature; and    -   wherein the dried stream comprises said C1 to C4 hydrocarbon        gases and from 0 ppm to 150 ppm water.

Various embodiments disclosed herein relate to a method of reducing themoisture content of a vapor stream comprising C1 to C4 hydrocarbon gasesand H₂O, by passing the vapor stream at subsonic velocity into an inletof a de Laval nozzle assembly, where the vapor stream has an initialtemperature of between 25° C. and 90° C. and an initial pressure ofbetween 150 psig and 1000 psig;

-   -   performing at least one step of producing a reduced-temperature        vapor stream in the de Laval nozzle assembly;    -   condensing H₂O from the reduced-temperature vapor stream to        produce a dried stream; and    -   recovering the condensed H₂O;    -   wherein said relative humidity of the vapor stream prior to        entering the de Laval nozzle is between about 2% and 100%, about        5% and about 95%, or about 20% and about 80%; and    -   wherein the dried stream comprises the C1 to C4 hydrocarbon        gases and from 0 ppm to 150 ppm water.

Various exemplary embodiments disclosed herein relate to a method ofdrying a vapor stream comprising C1 to C4 hydrocarbon gases by passingthe vapor stream at subsonic velocity into an inlet of a de Laval nozzleassembly, said vapor stream having an initial temperature of between 25°C. and 90° C., between 25° C. and 60°C., or between 25° C. and 40° C.and an initial pressure of between 150 psig and 1000 psig, wherein thevapor stream contains at least 500 ppm H₂O by volume;

-   -   wherein the partial pressure of H₂O in the vapor stream is up to        the vapor pressure of H₂O at the initial temperature;    -   the method comprising at least one step of producing a        reduced-temperature vapor stream in the de Laval nozzle        assembly;    -   condensing H₂O from the reduced-temperature vapor stream to        produce a dried stream; and    -   recovering the condensed H₂O;    -   wherein the dried stream comprises said C1 to C4 hydrocarbon        gases and from 0 ppm to 150 ppm water. In some embodiments, the        de Laval nozzle assembly is a single de Laval nozzle having a        throat, and is capable of accelerating the vapor stream to a        velocity of from Mach 1.5 to Mach 4, Mach 1.75 to Mach 3, or        Mach 2 to Mach 2.5. In some embodiments, the de Laval nozzle        assembly is at least two or more de Laval nozzles connected in        series, where the step of producing a reduced-temperature vapor        stream comprises:    -   accelerating said vapor stream to supersonic velocity in a first        de Laval nozzle to produce a first reduced-temperature vapor        stream;    -   passing the vapor stream from an outlet of said first de Laval        nozzle to an inlet of a second de Laval nozzle; and    -   accelerating said vapor stream to supersonic velocity in the        second de Laval nozzle to produce a second reduced-temperature        vapor stream. The step of recovering the condensed H₂O comprises        recovering the condensed H₂O from the first reduced-temperature        vapor stream and the second reduced-temperature vapor stream. In        some embodiments, the de Laval nozzle assembly is at least two        or more de Laval nozzles connected in parallel. In some        embodiments, the de Laval nozzle assembly comprises:    -   a low-temperature condenser, such as a water-cooled metal or        glass cold-finger or coiled tube condenser, which condenses a        portion of said H₂O from said vapor stream at subsonic velocity;        and    -   a de Laval nozzle which accelerates said vapor stream to        supersonic velocity to produce a reduced-temperature vapor        stream.

The C1 to C4 hydrocarbon gases to be dried may be ethane, ethene(ethylene), propane, propene (propylene), methylacetylene, propadiene,n-butane, isobutane, 1-butene, 2-butene, isobutylene, butadiene, MAPDgas (a methylacetylene-propadiene mixture), MAPP gas (amethylacetylene-propadiene-propane mixture), or a mixture thereof. TheC1 to C4 hydrocarbon gases to be dried may be propane, propene, or amixture thereof; or ethane, ethene, acetylene, or a mixture thereof. TheC1 to C4 hydrocarbon gases to be dried may comprise from 80 to 100% bymass of a mixture of C2 and C3 gases, in a C2 to C3 ratio of between 1:9and 9:1.

In various embodiments, the method of drying hydrocarbon gases comprisesa step of inducing swirling flow in said vapor stream prior torecovering the condensed H₂O. The method of drying hydrocarbon gases maycomprise a step of inducing swirling flow in said vapor stream prior toexpanding the vapor stream, or after expanding the vapor stream butbefore recovering the condensed H₂O. The swirling flow drives condensedH₂O toward the wall of said de Laval nozzle or the wall of a pipeconnected to an exit of said de Laval nozzle by centrifugal force,allowing recovery through an opening in the wall of the nozzle or thepipe.

After the C1 to C4 hydrocarbon gases are dried, C2 to C4 hydrocarbongases may be condensed from the dried gas stream by methods describedherein.

Various embodiments of the disclosed process are used for gasseparation. In particular, the process is directed towards condensing C3and/or C4 hydrocarbons and other heavy components from a gas streamcomprising C to C4 hydrocarbons, methane, oxygenated compounds(propanols, butyraldehydes, etc.), and various inorganic gases using aLaval nozzle; or for condensing water from a gas stream.

Various embodiments disclosed herein are directed to a method ofselectively recovering hydrocarbons with a boiling point of between−105° C. and 5° C. from a vapor stream. In some embodiments, the vaporstream may contain, based on the total weight of the hydrocarbon gases:

-   -   from 50% to 100% C3 hydrocarbons, from 70 to 100% C3        hydrocarbons, from 85 to 100% C3 hydrocarbons, or from 85% to        98% C3 hydrocarbons; and from 0% to 10% methane, from 0.5% to 5%        methane; or from 1% to 3% methane;    -   with the balance being C2 and C4 hydrocarbons.

In some embodiments, the vapor stream may contain, based on the totalweight of the hydrocarbon gases:

-   -   from 50% to 100% C4 hydrocarbons, from 70 to 100% C4        hydrocarbons, from 85 to 100% C4 hydrocarbons, or from 85% to        98% C4 hydrocarbons; and from 0% to 10% methane, from 0.5% to 5%        methane; or from 1% to 3% methane;    -   with the balance being C2 and C3 hydrocarbons.

In some embodiments, the vapor stream may contain greater than 50%,greater than 70%, or greater than 85% C2 hydrocarbons; and less than10%, less than 5%, or less than 3% methane, with the balance being C3and C4 hydrocarbons.

In various embodiments, the method comprises passing a vapor streamcomprising dried hydrocarbons with a boiling point of between −105° C.and 5° C. into an inlet of a de Laval nozzle having a throat, said vaporstream having an initial temperature of between 0° C. and 100° C. and aninitial pressure of between 200 psig and 500 psig; an initialtemperature of between 0° C. and 60° C. and an initial pressure ofbetween 250 psig and 400 psig; or an initial temperature of between 25°C. and 90° C., between 25° C. and 60° C., or between 25° C. and 40° C.and an initial pressure of between 275 psig and 325 psig;

-   -   expanding the vapor stream after the vapor stream passes through        the throat of the de Laval nozzle, producing a        reduced-temperature vapor stream;    -   condensing hydrocarbons with a boiling point of between −105° C.        and 5° C. from the reduced-temperature vapor stream as liquid        droplets; and    -   recovering the liquid droplets of condensed hydrocarbons from        the vapor stream.

In various embodiments, the liquid hydrocarbon droplets have a meandiameter of between 1.75×10−6 m and 2.5×10-6 m.

In various embodiments, the dried vapor stream comprises hydrocarbonswith a boiling point of between −40° C. and −60° C., i.e., propane,propene, and mixtures thereof, in an amount of between 85% and 100% byweight of the hydrocarbon gases. In other embodiments, the initial vaporstream comprises hydrocarbons with a boiling point of between −20° C.and 5° C., i.e., saturated C4 hydrocarbons, unsaturated C4 hydrocarbons,and mixtures thereof in an amount of between 70% and 100% by weight ofthe hydrocarbon gases. In some embodiments, the initial vapor streamcomprises hydrocarbons with a boiling point of between −105° C. and −85°C., i.e., ethane, ethene, and mixtures thereof, in an amount of between5% and 100% by weight of the hydrocarbon gases.

The C2 to C4 hydrocarbons may be saturated hydrocarbons, unsaturatedhydrocarbons, or a mixture thereof. At least a portion of the recoveredC2 to C4 hydrocarbons may be fed to the chemical reactor as a reactant.Alternatively, at least a portion of the condensed C2 to C4 hydrocarbonsmay be transferred to a recovery unit, such as a propane/propeneseparator, de-methanizer, or de-propanizer.

The recovered liquid C2 to C4 hydrocarbons may be fractionated bydistillation to produce a first fraction of C2 hydrocarbons with aboiling point of between −105°C. and −85° C.; a second fraction of C3hydrocarbons with a boiling point of between −40° C. and −60° C.; and athird fraction of C4 hydrocarbons with a boiling point of between −20°C. and 5° C. Where the waste gas is derived from a chemical reactor forproduction of butyraldehyde by hydroformylation or for production ofpolypropene, at least a portion of second fraction of C3 hydrocarbonsmay be recycled to the chemical hydroformylation reactor as a reactant.The C2 and C4 fractions may be fed to a cracking plant or anincinerator.

Alternatively, the C3 fraction boiling between −40° C. and −60° C. mayundergo further fractionation to produce a propane-rich fraction and apropene-rich fraction. This may be done by selective adsorption ofpropene onto a zeolite molecular sieve, or by distillation. If theinitial feed stream contains from 85% to 100% C3 hydrocarbon gases basedon the total weight of the hydrocarbon gases, fractionation of gasescondensed in the de Laval nozzle into a propane-rich fraction and apropene-rich fraction may be performed without requiring an initialfractionation into a first fraction of C2 hydrocarbons; a secondfraction of C3 hydrocarbons; and a third fraction of C4 hydrocarbons.The propene-rich fraction may be used as a reactant feed stream in achemical reactor, such as a hydroformylation reactor or a gas phasepolymerization reactor. The propane-rich fraction may be used as a feedstream for a cracking plant or an incinerator.

If the initial vapor stream is a waste gas from a chemical reactionusing propene as a starting material, e.g., hydroformylation of propeneto produce butyraldehyde or gas-phase propene polymerization, thepropene-rich fraction may be recycled to the reaction vessel as astarting material.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand various exemplary embodiments, referenceis made to the accompanying drawings, wherein:

FIG. 1 shows the change in gas temperature and in gas pressure as thegas accelerates through a de Laval nozzle.

FIG. 2A shows the equilibrium vapor pressure of propane as a function oftemperature.

FIG. 2B shows the equilibrium vapor pressure of ethane as a function oftemperature.

FIG. 2C shows the equilibrium vapor pressure of butane as a function oftemperature.

FIG. 3 compares the change in propane partial pressure in a de Lavalnozzle to the equilibrium vapor pressure of propane.

FIG. 4 shows separation of propane from an ethane/propane mixture in ade Laval nozzle, where propane begins condensation at Mach ˜1.4 andethane begins condensation at Mach ˜2.

FIG. 5 shows condensation of butane from a 20:80 butane/propane mixturein a de Laval nozzle, where butane begins condensation at Mach ˜1.5 andpropane begins condensation at Mach ˜1.6.

FIG. 6 shows condensation of butane from a 35:65 butane/propane mixturein a de Laval nozzle, where butane begins condensation at Mach 1.1 to1.2 and propane begins condensation at Mach ˜1.9.

FIG. 7 shows condensation of water from a propane stream containing 1.5%water vapor in a de Laval nozzle, where water begins condensation atMach ˜1.1 and propane begins condensation at Mach ˜1.9.

FIG. 8 shows condensation of water from a hydrocarbon stream containing4000 ppm water in a de Laval nozzle, where water concentration decreasesfrom 4000 ppm at the nozzle throat to less than 10 ppm.

DETAILED DESCRIPTION

Use of De Laval Nozzles in Gas Separation

Supersonic separation methods operate by accelerating a gas mixture tosupersonic speeds by passing the mixture through a converging-divergingnozzle. The expansion process lowers the temperature and pressure of thegas mixture. If the partial pressure of a condensable component in thevapor is decreased below the vapor pressure of that component at thelocal temperature, homogeneous nucleation can commence, initiating theformation of small droplets of the condensate that may then grow viacondensation and coagulation mechanisms. These droplets are typicallyvery small (of the order of 0.1 microns) and generally travel with thespeed of the gas. To collect these droplets, supersonic separatorsutilize swirl vanes and other devices to induce centripetal accelerationof the droplets toward the nozzle walls, where they may be captured. Theswirling devices also increase local turbulence levels within theseparator, greatly increasing the probability of droplet-dropletcollisions which lead to larger droplet volumes and enhanced potentialfor collection.

The current disclosure is directed toward practical utilities of a deLaval nozzle, or convergent-divergent nozzle, in gas separation. Invarious embodiments disclosed herein, a stream of gases or a mixture ofgas and vapor passes through a de Laval nozzle. The nozzle has anaxisymmetric hourglass shape, pinched in the middle.

As gas passes through the pinched portion of the nozzle (the throat),its velocity increases. At the throat of the de Laval nozzle, gasvelocity c is equal to the square root of γRT (signified as √γRT), whereγ is a constant for a particular gas or gas mixture. The parameter γ maychange if the composition of the gas changes as it passes the de Lavalnozzle. For this model it is assumed that γ is a constant dependent onthe nature of the gas. For hydrocarbon mixtures, γ is ˜1.3, while forair, γ is ˜1.4. In the following discussion, temperature will bereported in degrees K, and pressure in bar, defined as equal to 0.1 Mpaor 0.987 atm.

At the throat of the de Laval nozzle, the gas velocity reaches sonicvelocity, i.e., the velocity c=Mach 1. At Mach 1, (c/√γRT)=1. Prior toentering the throat, gas velocity c is subsonic, i.e., (c/√γRT)<1; whileafter exiting the throat, gas velocity c is supersonic, i.e.,(c/√γRT) >1. It has been demonstrated that temperature of a gas in a deLaval nozzle is dependent on γ and on gas velocity, measured in terms ofMach number M, where M=(c/√γRT). Temperature of a gas in a de Lavalnozzle, reported in terms of the ratio between the temperature of gaswithin the nozzle, T, and the initial gas temperature prior to enteringthe nozzle T_(o), is given by Equation (1):

T/T _(o)=1/(1+KM ²)  (1)

where:

-   -   K=(γ−1)/2

Similarly, pressure of a gas in a de Laval nozzle, reported in terms ofthe ratio between the pressure of gas within the nozzle, P, and theinitial gas temperature prior to entering the nozzle P_(o), is given byEquation (2):

P/P _(o)=[1/(1+KM ²)]^(X)  (2)

where:

-   -   K=(γ−1)/2 and X=γ/(γ−1)

For hydrocarbon mixtures, where γ is ˜1.3, K=0.15 and X=4.33; for air,where γ is ˜1.4, K=0.2 and X=3.5.

As the gas leaves the nozzle at supersonic speed, both pressure andtemperature fall. The change in pressure and temperature as a functionof gas velocity (reported as a Mach value) is presented in Table 1 belowfor both air and hydrocarbon gases, at velocities of up to Mach 4; datafor T/T_(o) and P/P_(o) is shown as a function of Mach number M in FIG.1.

FIG. 1 shows that air temperature decreases more rapidly thanhydrocarbon gas temperature as it accelerates through the de Lavalnozzle. However, the change in air pressure and in hydrocarbon gaspressure in a de Laval nozzle is, for all practical purposes, identical.

TABLE 1 Pressure and temperature as a function of gas velocity in a deLaval nozzle. Velocity T/T_(o) T/T_(o) P/P_(o) P/P_(o) T (Air, T (HC,(Mach) (γ = 1.4) (γ = 1.3) (γ = 1.4) (γ = 1.3) ° K)¹ ° K)² 0.2 0.9920.994 0.972 0.974 310.5 311.1 0.4 0.969 0.977 0.896 0.904 303.3 305.80.6 0.932 0.949 0.782 0.797 291.7 297.0 0.8 0.887 0.912 0.657 0.671277.6 285.5 1.0 0.833 0.870 0.528 0.547 260.7 272.3 1.2 0.776 0.8220.412 0.428 242.9 257.3 1.4 0.718 0.773 0.313 0.328 224.7 241.9 1.60.661 0.723 0.235 0.246 206.9 226.3 1.8 0.607 0.673 0.174 0.180 190.0210.6 2.0 0.556 0.625 0.128 0.131 174.0 195.6 2.5 0.444 0.516 0.0580.057 139.0 161.5 3.0 0.357 0.425 0.027 0.025 111.7 133.0 4.0 0.2380.294 0.007 0.005 74.5 92.0 Initial temperature T_(o) = 313° K. HC =hydrocarbons; initial temperature T_(o) = 313° K.

During passage of a gas mixture through a de Laval nozzle, gases derivedfrom higher boiling materials may condense as a liquid, whilelow-boiling gases are recovered as gases. This is due to the change inequilibrium vapor pressure as the temperature drops after the gas exitsthe nozzle; if temperature drops to a point T₁ where the vapor pressureof the gas is greater than the equilibrium vapor pressure of that gas attemperature T₁, the gas will begin to condense so as to achieve anequilibrium between the liquid and vapor phases. Since pressure andtemperature are changing rapidly in the accelerating gas stream; due tothe rapidly changing conditions, a liquid/vapor equilibrium cannot beachieved in the accelerating gas stream. As the pressure decreases,further nucleation occurs.

During condensation, fine liquid droplets nucleate and grow. The streamof gases is subjected to a vortex chamber or similar device, whichcauses vapors to swirl around a central axis as they leave the nozzle;centrifugal forces aid in separation of condensed droplets of liquefiedgas from the gas or vapor stream.

Methane, at a starting pressure of 21 bar and a starting temperature of313° K, achieves:

-   -   a pressure of 0.53 bar and a temperature of 133° K at Mach 3;        and    -   a pressure of 0.11 bar and a temperature of 92° K at Mach 4.

At 133° K, the equilibrium vapor pressure for methane is about 5 bar.Similarly, at 92° K, the equilibrium vapor pressure for methane is about0.45 bar. Since the equilibrium vapor pressure for methane, atsupersonic gas velocities of up to Mach 4, exceeds the actual pressureachieved in a supersonic gas stream, methane does not undergocondensation in supersonic gas streams. Thus, methane, in this model, isconsidered to be a non-condensable gas.

Recovery and Recycling of Hydrocarbon Gases

The current disclosure is directed to recovery and reuse or recycling ofcondensable hydrocarbons from a mixture of methane or othernon-condensable gases and condensable hydrocarbons. Additionally, thecurrent disclosure is directed to fractionation of mixtures ofcondensable gases, such as water vapor and/or C2 to C4 hydrocarbons,using de Laval nozzles. The current disclosure is further directed torecovery and/or recycling of purified condensable gases from mixtures ofgases using de Laval nozzles.

Various embodiments of the disclosed process are used for gasseparation. In particular, the process is directed towards condensing C3hydrocarbons and other heavy components from a gas stream comprising C3hydrocarbons, methane, oxygenated compounds (propanols, butyraldehydes,etc.), and various inorganic gases using a Laval nozzle.

In embodiments directed to gas separation, a stream of gases or amixture of gas and vapor passes through a de Laval nozzle, andaccelerates to supersonic speed (c >Mach 1). As the gas leaves thenozzle at supersonic speed, both pressure and temperature fall. Gasesderived from higher boiling materials condense as a liquid, andlow-boiling gases are recovered as gases. The stream of gases issubjected to a vortex chamber or similar device, which causes vapors toswirl around a central axis as they leave the nozzle; centrifugal forcesaid in separation of condensed gases from the gas or vapor stream.

Various embodiments relate to treatment of a gas stream from ahydroformylation reaction process, where propene (propylene) gas reactswith hydrogen and carbon monoxide to produce butyraldehydes. These gasstreams may comprise the following streams, where the Oxo Purge Streamcomes from hydroformylation with a conventional rhodium-containinghydroformylation catalyst, such as tris(triphenylphosphine)rhodiumcarbonyl hydride, with the formula RhH(PPh₃)₃CO. Under certainconditions, the purge stream from a hydroformylation reactor may becarried out relatively low pressure for the preparation of highproportions of n-butyraldehyde from propene, using techniques describedin, for example, U.S. Pat. Nos. 4,694,109; 4,742,178; and 5,026,886,incorporated herein by reference.

As can be seen from the chart below, the low pressure hydroformylationpurge stream in this model can potentially contain a high concentrationof propene. A method of effectively recovering this unreacted startingmaterial would be desirable.

Amount (Oxo Purge; Amount (Low Pressure Compound mole %) Oxo Purge;weight %) Hydrogen 44 8 Nitrogen 15 3.3 Argon — 1 Carbon monoxide 12.6 3Carbon dioxide 2.7 — Methane 2.8 2.9 Ethane 0.5 — Propene 21 58 Propane1.4 20 Butyraldehydes — 3.8

In various embodiments, the Oxo Purge gas stream, the low pressure OxoPurge gas stream, or a mixture thereof is taken from ahydrocarboxylations reaction process and passed through a de Lavalnozzle. As the gas stream exits the de Laval nozzle with a swirling flowpattern, propene (boiling point: −47.6° C.), propane (boiling point:−42.2° C.), and butyraldehydes condense as a liquid and are recovered asa liquid sidestream from a pipe exiting the de Laval nozzle. The othergases are not condensed, and leave the pipe exiting the de Laval nozzleas a gas.

The gas stream may enter the de Laval nozzle at a temperature of about0° C. to 100° C., 0° C. to 60° C., 20° C. to 40° C., or 40° C.; and apressure of about 200 to 500 psig, about 250 to 450 psig, or about 305psig

Drying of Hydrocarbon Gases

Various embodiments disclosed herein are directed to a method of dryingvolatile hydrocarbon gases in a vapor stream. Various embodiments aredirected to drying of wet ethene gas, wet propene gas, or a wet mixtureof C1 to C4 alkanes, where the supply pressure is between 7 and 1400psig, the supply temperature is between 5° C. and 50° C.; and therelative humidity is between 5% and 95%.

In some embodiments, the vapor stream may contain, based on the weightof the hydrocarbon gases:

-   -   from 50% to 100% C3 hydrocarbons, from 70 to 100% C3        hydrocarbons, from 85 to 100% C3 hydrocarbons, or from 85% to        98% C3 hydrocarbons;    -   from 0% to 10% methane, from 0.5% to 5% methane; or from 1% to        3% methane; and    -   from 100 ppm to 100,000 ppm water, from 500 ppm to 10,000 ppm        water; or    -   from 1000 ppm to 5,000 ppm water, with the balance being C2 and        C4 hydrocarbons.

In some embodiments, the vapor stream may contain, based on the weightof the hydrocarbon gases:

-   -   from 50% to 100% C4 hydrocarbons, from 70 to 100% C4        hydrocarbons, from 85 to 100% C4 hydrocarbons, or from 85% to        98% C4 hydrocarbons;    -   from 1% to 10% methane, from 0.5% to 5% methane; or from 1% to        3% methane; and    -   from 100 ppm to 100,000 ppm water, from 500 ppm to 10,000 ppm        water, or    -   from 1000 ppm to 5,000 ppm water,    -   with the balance being C2 and C3 hydrocarbons.

In some embodiments, the vapor stream may contain greater than 50%,greater than 70%, or greater than 85% C2 hydrocarbons; up to 100,000 ppmwater, up to 10,000 ppm water, or from up to 5,000 ppm water; and lessthan 10%, less than 5%, or less than 3% methane, with the balance beingC3 and C4 hydrocarbons.

Various embodiments disclosed herein relate to a method of drying avapor stream comprising C1 to C4 hydrocarbon gases, by passing a vaporstream comprising such hydrocarbon gases into an inlet of a de Lavalnozzle having a throat, said vapor stream having an initial temperatureof between 0° C. and 100° C.; between 10° C. and 60° C.; an initialtemperature of between 5° C. and 50° C.; or an initial temperature ofbetween 20° C. and 40° C.; and an initial pressure of between 150 psigand 1000 psig, between 300 psig and 800 psig; between 200 psig and 500psig, or between 500 psig and 1000 psig;

-   -   expanding the vapor stream after the vapor stream passes through        the throat of the de Laval nozzle, producing a        reduced-temperature vapor stream; condensing water from the        reduced-temperature vapor stream to produce a dried stream; and    -   recovering the condensed H₂O from said vapor stream;    -   wherein the dried stream comprises C1 to C4 hydrocarbon gases        and from 0 ppm to 10 ppm water.

In various embodiments, the C1 to C4 hydrocarbon gases are selected fromthe group consisting of C2 hydrocarbons, C3 hydrocarbons, C4hydrocarbons, and mixtures thereof. The C1 to C4 hydrocarbon gases maybe C3 gases selected from the group consisting of propane, propene,propyne, and mixtures thereof. The C1 to C4 hydrocarbon gases may be C2gases selected from the group consisting of ethane, ethene, acetylene,and mixtures thereof. The C1 to C4 hydrocarbon gases may comprise from80 to 100% by mass of a mixture of C2 and C3 gases, in a C2 to C3 ratioof between 1:9 and 9:1, between 1:4 and 4:1, between 2:3 and 3:2, or1:1. The C1 to C4 hydrocarbon gases may comprise from 80 to 1000% bymass of C3 gases; or from 80 to 100% by mass of C2 gases.

Recovery of Dried Hydrocarbon Gases

Various embodiments disclosed herein are directed to a method of dryingvolatile hydrocarbon gases in a vapor stream, and recovering dried gasesfrom the vapor stream. In some embodiments, the initial vapor stream maycontain, based on the weight of the hydrocarbon gases:

-   -   from 50%9′ to 1000 to C3 hydrocarbons, from 70 to 100% C3        hydrocarbons, from 85 to 100% C3 hydrocarbons, or from 85% to        98% C3 hydrocarbons;    -   from 1% to 10% methane, from 0.5% to 5% methane; or from 1% to        3% methane; and    -   from 100 ppm to 100,000 ppm water, from 500 ppm to 10,000 ppm        water, or    -   from 1000 ppm to 5,000 ppm water, with the balance being C2 and        C4 hydrocarbons.

In some embodiments, the vapor stream may contain, based on the weightof the hydrocarbon gases:

-   -   from 50% to 100% C4 hydrocarbons, from 70 to 100% C4        hydrocarbons, from 85 to 100% C4 hydrocarbons, or from 85% to        98% C4 hydrocarbons;    -   from 1% to 10% methane, from 0.5% to 5% methane; or from 1% to        3% methane; and    -   from 100 ppm to 100,000 ppm water, from 500 ppm to 10,000 ppm        water, or    -   from 1000 ppm to 5,000 ppm water, with the balance being C2 and        C3 hydrocarbons.

In some embodiments, the vapor stream may contain greater than 50%,greater than 70%, or greater than 85% C2 hydrocarbons; up to 100,000 ppmwater, up to 10,000 ppm water, or from up to 5,000 ppm water; and lessthan 10%, less than 5%, or less than 3% methane, with the balance beingC3 and C4 hydrocarbons.

Various embodiments disclosed herein relate to a method of recoveringdried hydrocarbon gases in a vapor stream comprising C1 to C4hydrocarbon gases, by first drying the vapor stream, and then condensingthe desired hydrocarbon gases from the vapor stream.

According to various embodiments disclosed herein, the drying stepinvolves passing a vapor stream comprising C1 to C4 hydrocarbon gasesand up to 100,000 ppm water into an inlet of a de Laval nozzle having athroat, where the vapor stream having an initial temperature of between0° C. and 100° C.; between 10° C. and 60° C.; or an initial temperatureof between 20° C. and 40° C.; and an initial pressure of between 150psig and 1000 psig;

-   -   expanding the vapor stream after the vapor stream passes through        the throat of the de Laval nozzle, producing a        reduced-temperature vapor stream;    -   condensing water from the reduced-temperature vapor stream to        produce a dried stream; and    -   recovering the condensed H₂O from said vapor stream to produce a        dried stream; where the dried stream comprises C1 to C4        hydrocarbon gases and from 0 ppm to 10 ppm water.

In various embodiments, the method further comprises a step of inducingswirling flow in the vapor stream prior to expanding, or after expandingbut before recovering; so that the swirling flow drives the condensedwater toward the wall of the de Laval nozzle or the wall of a pipeconnected to an exit of the de Laval nozzle by centrifugal force.

In a second step, the dried stream is passed into an inlet of a de Lavalnozzle having a throat, at an initial temperature of between 0° C. and100° C. and an initial pressure of between 200 psig and 500 psig. Thedried stream is expanded after the vapor stream passes through thethroat of the de Laval nozzle, producing a second reduced-temperaturestream; and C1 to C4 hydrocarbons then condense from the secondreduced-temperature stream as liquid droplets; and are recovered ascondensed droplets of dried C1 to C4 hydrocarbons from thereduced-temperature stream.

The droplets of dried C1 to C4 hydrocarbons may be fed directly to achemical reactor as a reactant feed. In some embodiments, the initialvapor stream is a waste gas stream from a chemical reactor, and thedroplets of dried C1 to C4 hydrocarbons are recycled to a chemicalreactor, where the chemical reactor may be a hydroformylation reactor ora gas phase polymerization reactor.

Some embodiments are directed to drying and recovering C3 hydrocarbongases in a vapor stream from a chemical reactor, where the vapor streamcomprises 85% to 100% by weight C3 hydrocarbon gases. The methodinvolves drying the vapor stream comprising the C3 hydrocarbon gases toproduce a dried stream; passing the dried stream into an inlet of a deLaval nozzle having a throat, said dried stream having an initialtemperature of between 0° C. and 100° C. and an initial pressure ofbetween 200 psig and 500 psig;

-   -   expanding the dried stream after the vapor stream passes through        the throat of the de Laval nozzle, producing a second        reduced-temperature stream;    -   condensing C3 hydrocarbon gases from the second        reduced-temperature stream as liquid droplets; and either:    -   directly recycling a portion of the condensed C3 hydrocarbon        gases to the chemical reactor, or    -   separating the condensed C3 hydrocarbon gases into a        propane-rich fraction and a propene-rich fraction; and recycling        a portion of the propene-rich fraction to the chemical reactor.

According to various embodiments disclosed herein, the propane feedstream may used as a feed stream for a cracking reactor; or the propanefeed stream may be used in a feed stream for an incinerator.

Fractionation of C2 to C4 Hydrocarbon Gases

According to various embodiments disclosed herein, hydrocarbons in a gasstream comprising a first hydrocarbon having 2 or 3 carbon atoms, and asecond hydrocarbon having 3 or 4 carbon atoms, where the first andsecond hydrocarbons do not both have 3 carbon atoms, may befractionated. According to this method, the gas stream is passed into aninlet of a de Laval nozzle having a throat, where the gas stream has aninitial temperature of between 0° C. and 100° C. and an initial pressureof between 200 psig and 500 psig. The gas stream expands after passingthrough the throat of the dc Laval nozzle, producing areduced-temperature stream. A fraction enriched in the secondhydrocarbon condenses from the reduced-temperature stream as liquiddroplets, and is recovered as a liquid. A gaseous fraction enriched inthe first hydrocarbon exits the outlet of the de Laval nozzle, and maybe recovered.

The gas stream to be fractionated may, for example, comprise ethane andpropane, propane or butane, or ethane and butane. The first hydrocarbonmay be ethane, ethene, or a mixture thereof; or propane, propene, or amixture thereof. The first hydrocarbon may be ethane, ethene, or amixture thereof, or propane, propene, or a mixture thereof. The secondhydrocarbon may be propane, propene, methylacetylene, propadiene, MAPD(a mixture of methylacetylene and propadiene), or a mixture thereof, orbutane, 1-butene, 2-butene, isobutane, isobutylene, butadiene, or amixture thereof.

Gas Separation Examples

Several practical applications of de Laval nozzles in gas separation arenow described in the following examples.

Example 1: Separation of Propane from a Propane/Air Mixture

Separation of propane from a gas stream of mixture of air and propanegas may be accomplished using a de Laval nozzle, where the gas-stream isat an initial pressure of 21 bar, and an initial temperature of 313° K.The gas mixture contains 20 mol % propane at partial pressure P₁ and 80mol % air at partial pressure P₂; by the relationship P=P₁+P₂, themixture under these initial conditions contains air at a partialpressure of 16.8 bar and propane at a partial pressure of 4.2 bar. Sincethe mixture is predominantly air, γ is assumed to be ˜1.4.

FIG. 2A shows the equilibrium vapor pressure of propane (bar) as afunction of temperature (degrees K). Table 2 shows the change intemperature and propane partial pressure as the gas accelerates fromMach 1, at the nozzle throat, to Mach 2.

TABLE 2 Propane Partial Pressure (Bar) in a de Laval Nozzle. PropanePropane Velocity T (Air, P/P_(o) Partial Equilibrium (Mach) degrees K)(γ = 1.4) Pressure Vapor Pressure 1.0 260.7 0.528 2.21 3 1.2 242.9 0.4121.73 1.7 1.4 224.7 0.313 1.31 0.8 1.6 206.9 0.235 0.99 0.3 1.8 190.00.174 0.73 0.15 2.0 174.0 0.128 0.54 0.035

Table 2, in columns 2 and 3 show the change in temperature and the ratioof pressure P to initial pressure P_(o) as the gas accelerates from Mach1, at the nozzle throat, to Mach 2 (T_(o)=313° K). Column 4 shows thepropane partial pressure in gas mixture of 80% air and 20% propane gasas it travels through a de Laval nozzle, in the absence of condensation,based on an initial partial pressure of 4.2 bar. Column 5 shows theequilibrium vapor pressure of propane as a function of temperature. Atthe throat of the nozzle (Mach 1), the partial pressure of propane inthe gas stream is less than the equilibrium vapor pressure of propane atthe local temperature, i.e., in the throat). Similarly, at Mach 1.2, thepartial pressure of propane in the gas stream is approximately equal tothe equilibrium vapor pressure of propane. Between Mach 1.4 and Mach2.0, the partial pressure of propane in the gas stream exceeds theequilibrium vapor pressure of propane, and condensation of excesspropane vapor occurs, as shown in FIG. 3. Thus, prior to Mach 1.2, thepropane partial pressure in the gas stream is given by Equation (2) asset forth above, and propane condensation does not occur.

After the gas stream reaches Mach 1.2, the propane partial pressure inthe gas stream exceeds the equilibrium vapor pressure of propane, andpropane condensation occurs. If the system was allowed to reachequilibrium at a velocity greater than Mach 1.2, propane would condensefrom the gas stream until the propane partial pressure in the gas streamwas equal to the equilibrium vapor pressure. Thus, after Mach 1.2, theactual propane partial pressure in the gas stream is less than thepressure given by Equation (2), due to propane condensation from the gasstream. At the same time, since the gas stream is a non-equilibriumenvironment, the actual propane partial pressure in the gas stream isgreater than the equilibrium vapor pressure of propane.

If the gas stream was allowed to reach equilibrium under conditions oftemperature and pressure prevailing at Mach 2.0, approximately 93.5% ofthe propane gas would condense as a liquid. Condensation would reducethe propane partial pressure of 0.54 bar to the equilibrium vaporpressure of 0.035 bar. However, as a result of the rapidly changingtemperature and pressure in the gas stream, equilibrium is not achievedand only a portion of this gas is recovered. In general, recovery ofabout 12% by weight to about 40% by weight of the propane in a gasstream by condensation in a de Laval nozzle is considered acceptable.Recovery can be increased by passing a gas stream through multiple deLaval nozzles in series, i.e., two de Laval nozzles in series, three deLaval nozzles in series, four de Laval nozzles in series, or more deLaval nozzles in series.

Example 2. Separation of Propane from a Propane/Ethane Mixture

Use of a de Laval nozzle also allows separation of propane from amixture of ethane gas and propane gas at an initial pressure of 21 bar,and an initial temperature of 313° K. The gas mixture contains 20 mol %propane at partial pressure P₁ and 80 mol % propane at partial pressureP₂; by the relationship P=P₁+P₂, the mixture under these initialconditions contains ethane at a partial pressure of 16.8 bar and propaneat a partial pressure of 4.2 bar. The term γ is assumed to besubstantially constant at ˜1.3, as the mixture is a mixture ofhydrocarbon gases.

FIG. 2A and FIG. 2B shows the equilibrium vapor pressures of propane andethane (bar), respectively, as a function of temperature (degrees K).Table 3 presents the change in temperature and partial pressures as thegas accelerates from Mach 1, at the nozzle throat, to Mach 3. At thenozzle throat (Gas velocity c=Mach 1), the partial pressures of ethaneand propane in the vapor stream are each less than the equilibrium vaporpressure. At Mach 1.6, the partial pressure of propane in the vaporstream exceeds the equilibrium vapor pressure of propane, and propanebegins to condense from the vapor stream as liquid droplets. At Mach1.6, the partial pressure of ethane in the vapor stream is less than theequilibrium vapor pressure of ethane, and ethane does not condense.Ethane does not condense until about Mach 2, as shown in the graph inFIG. 4. This allows substantially pure propane to be separated from anethane/propane mixture, using a de Laval nozzle designed to accelerategas to Mach 2. Even if a longer de Laval nozzle, designed to accelerategas to Mach 2.5, is used, an ethane/propane mixture can be fractionatedinto:

-   -   1) a propane-rich fraction recovered as a liquid; and    -   2) an ethane-rich gaseous fraction recovered at the outlet of        the de Laval nozzle

TABLE 3 Propane Partial Pressure (Bar) in a Propane/Ethane MixtureEquilibrium Partial Pressure Vapor Pressure Velocity c T (bar) (bar)(Mach) (° K)¹ P/P_(o) C₃H₈ C₂H₆ C₃H₈ C₂H₆ 1.0 272.3 0.547 2.30 9.19 4.525 1.2 257.3 0.428 1.78 7.19 3 17 1.4 241.9 0.328 1.38 5.51 1.5 12 1.6226.3 0.246 1.03 4.20 0.8 7 1.8 210.6 0.180 0.76 3.02 0.35 4 2.0 195.60.131 0.55 2.20 0.15 2 2.5 161.5 0.057 0.24 0.96 0.01 0.25 3.0 133.00.025 0.11 0.42 — 0.02 ¹Initial temperature T_(o) = 313° K.

Example 3. Separation of C3 Hydrocarbons from a Hydroformylation WasteGas

Stream

A simulated process purge stream was examined in the supersonicseparator model, where the stream contains the following gases,expressed in terms of mol % of the total: Hydrogen 43%, nitrogen 14%,carbon monoxide 13%, carbon dioxide 3%, methane 3%, ethane 0.5%, propane21%, and propene 1.5%. Thus, about 86% of the hydrocarbon gases were C3hydrocarbons (propane and propene). The process stream was simulated at305 psig [21.03 bar (g)] and a flow rate of 40 thousand standard cubicfeet per minute. Table 4 shows the C3 fraction recovery as a function offeed temperature. The C3 recovery is defined as mass fraction of C3s inliquid relative to the total C3s in feed. Each stage of C3 hydrocarbonseparation from a supersonic gas stream was modeled in a bench-scale deLaval nozzle capable of a ˜Mach 2 expansion.

TABLE 4 C3 Recovery from a Hydroformylation Waste Stream FeedTemperature C3 Recovery (C.) (%) 40 17 20 28 0 39

Table 4 shows that a reduction in feed temperature increases C3recovery. Moreover, the concentration of C3s in the liquid hydrocarbonsrecovered from the liquid outlet of the de Laval nozzle was 99.9 mole %.

A second simulation was performed to study the effect of staging at afeed temperature of 20° C., where each stage involves passage through ade Laval nozzle. Only one additional stage of supersonic separation wasused, as shown in Table 5. Table 5 show that addition of a second nozzlein series results in improved C3 recovery. The overall mass flow rate intwo stages is different, mainly due to reduced C3 mass in stage 2.

TABLE 5 Multistage C3 Recovery from a Hydroformylation Waste Stream FeedTemperature (degrees C.) 20 Hydrocarbon composition of Stage 1 feed86.5% C3; 13.5% C1 to C2 C3 Recovery [Stage 1] (%) 28 Hydrocarboncomposition of Stage 2 feed 77.8% C3; 22.2% C1 to C2 C3 Recovery [Stage2] (%) 37

The model demonstrates the effective recovery for C3 hydrocarbons in 2stage of separation is ˜50% to 55% for this simulated process stream,using two stages of supersonic separation in a de Laval nozzle. In theExample of Table 4, 28% of the C3 hydrocarbons in the initial feed arerecovered as a liquid from stage 1. The non-condensed gas stream exitingthe stage 1 de Laval nozzle serves as a feed stream for the stage 2 deLaval nozzle. In the second stage, 37% of the C3 hydrocarbons in thestage 2 feed are recovered as a liquid, for a total recovery from stages1 and 2 of 53% of the C3 hydrocarbons in the initial feed. In principle,recovery can be further enhanced through the use of three, four, or morede Laval nozzles in series.

Example 4. Separation of Butane from a Propane/Butane Mixture (InitialPressure: 21 Bar)

Separation of butane from a mixture of propane gas and butane gas at aninitial pressure of 21 bar, and an initial temperature of 373° K may beaccomplished in a de Laval nozzle, under the proper conditions. The gasmixture contains 20 mol % butane at partial pressure P₁ and 80 mol %propane at partial pressure P₂; by the relationship P=P₁+P₂ the mixtureunder these initial conditions contains ethane at a partial pressure of16.8 bar and propane at a partial pressure of 4.2 bar, where, the term γis assumed to be substantially constant at ˜1.3.

FIG. 2A and FIG. 2C shows the equilibrium vapor pressures of propane andbutane (bar), respectively, as a function of temperature (degrees K).Table 6 presents the change in temperature and partial pressures as thepropane/butane gas mixture accelerates from Mach 1, at the nozzlethroat, to Mach 2.5. At the nozzle throat (Gas velocity c=Mach 1), thepartial pressures of butane and propane in the vapor stream are eachless than the equilibrium vapor pressure. At Mach 1.6, the partialpressure of butane in the vapor stream exceeds the equilibrium vaporpressure of propane, and butane begins to condense from the vapor streamas liquid droplets. At Mach 1.8, the partial pressure of propane in thevapor stream exceeds the equilibrium vapor pressure of propane, andpropane condenses. This is shown in the graph in FIG. 5. Under theseconditions, it is difficult to achieve good separation between propaneand butane in a de Laval nozzle.

TABLE 6 Partial Pressure (Bar) in a Butane (20 mol %)/Propane (80 mol %)Mixture Equilibrium Partial Pressure Vapor Pressure Velocity T (bar)(bar) (Mach) (° K)² P/P_(o) C₄H₁₀ C₃H₈ C₄H₁₀ C₃H₈ 1.0 324.5 0.547 2.309.19 4.7 20 1.2 306.6 0.428 1.78 7.19 3 13 1.4 288.3 0.328 1.38 5.51 1.88 1.6 269.7 0.246 1.03 4.20 0.9 4.5 1.8 251.0 0.180 0.76 3.02 0.45 2.22.0 233.1 0.131 0.55 2.20 0.18 1.2 2.5 192.5 0.057 0.24 0.96 0.01 0.13²Initial temperature T_(o) = 373° K.

Improved separation can be achieved by manipulating the conditions ofgas concentration and gas pressure. For example, a mixture of propanegas and butane gas at an initial pressure of 21 bar, and an initialtemperature of 373° K, may be separated if the amount of butane in thegas mixture is increased. For example, a gas mixture containing 35 mol %butane at partial pressure P₁ and 65 mol % propane at partial pressureP₂ may be separated.

Table 7 presents the change in temperature and partial pressures as the65% propane/35% butane gas mixture accelerates from Mach 1, at thenozzle throat, to Mach 2.5. At Mach 1.2, the partial pressure of butanein the vapor stream exceeds the equilibrium vapor pressure of butane,and butane begins to condense from the vapor stream as liquid droplets,as shown in FIG. 6. Propane does not begin to condense until nearly Mach1.8. By increasing butane concentration in the vapor stream, it becomespossible to achieve good separation between propane and butane in a deLaval nozzle.

TABLE 7 Partial Pressure (Bar) in a Butane (35 mol %)/Propane (65 mol %)Mixture Equilibrium Partial Pressure Vapor Pressure Velocity T (bar)(bar) (Mach) (° K)³ P/P_(o) C₄H₁₀ C₃H₈ C₄H₁₀ C₃H₈ 1.0 324.5 0.547 4.047.51 4.7 20 1.2 306.6 0.428 3.16 5.60 3 13 1.4 288.3 0.328 2.22 4.50 1.88 1.6 269.7 0.246 1.83 3.41 0.9 4.5 1.8 251.0 0.180 1.32 2.55 0.45 2.22.0 233.1 0.131 0.96 1.77 0.18 1.2 2.5 192.5 0.057 0.42 0.78 0.01 0.13³Initial temperature T_(o) = 373° K.

Example 5. Drying of a Propane Stream Containing 1.5% Water (InitialPressure: 11 Bar)

Water may be separated from a propane gas stream using a de Lavalnozzle. As an example, a propane stream containing 1.5% by volume watervapor may be accelerated through a de Laval nozzle, where the propanestream is at an initial pressure of 11 bar, and an initial temperatureof 373° K. The gas mixture contains 1.5 mol % water at partial pressureP₁, and 98.5 mol % propane at partial pressure P₂; by the relationshipP=P₁+P₂, the mixture under these initial conditions contains water at apartial pressure of 0.17 bar and propane at a partial pressure of 10.83bar, where the term γ is assumed to be substantially constant at ˜1.3.

Table 8 presents the change in temperature and partial pressures as thepropane/water vapor gas mixture accelerates from Mach 1, at the nozzlethroat, to Mach 2.5. At the nozzle throat (Gas velocity c=Mach 1), thepartial pressures of water and propane in the vapor stream are each lessthan the equilibrium vapor pressure. At Mach 1.2, the partial pressureof water in the vapor stream exceeds the equilibrium water vaporpressure, and liquid water begins to condense from the vapor stream.Under these conditions, the partial pressure of propane in the vaporstream exceeds the equilibrium propane vapor pressure at about Mach 2,and propane condenses. Under these conditions, it is easy to removesubstantially all water from a moist propane stream. FIG. 7 showscondensation of water from a propane stream containing 1.5% water vaporin a de Laval nozzle, where water begins condensation at Mach ˜1.1 andpropane begins condensation at Mach ˜1.9.

TABLE 8 Partial Pressure (Bar) in a Water (1.5 mol %)/Propane (98.5 mol%) Mixture (Initial Pressure: 11 bar) Equilibrium Partial Pressure VaporPressure Velocity T (bar) (bar) (Mach) (° K)⁴ P/P_(o) H₂O C₃H₈ H₂O C₃H₈1.0 324.5 0.547 0.088 5.92 0.132 20 1.2 306.6 0.428 0.073 4.62 0.052 131.4 288.3 0.328 0.052 3.55 0.017 8 1.6 269.7 0.246 0.042 2.65 0.005 4.51.8 251.0 0.180 0.031 1.94 0.001 2.2 2.0 233.1 0.131 0.021 1.41 0.00021.2 2.5 192.5 0.057 0.010 0.61 — 0.13 ⁴Initial temperature T_(o) = 373°K.

Example 6. Drying of a Propene Stream Containing 0.2% Water (InitialPressure: 13.2 Bar)

A propene gas stream containing 2000 ppm (0.2%) water vapor was modeled,with a starting pressure of 191 psig [13.2 bar (g)] and a startingtemperature of 300.4° K. The gas stream was tested in a bench-scale deLaval nozzle capable of a ˜Mach 2 expansion.

The propene gas exiting the de Laval nozzle was substantially dry. Nearcomplete nucleation of the water to form a liquid phase had occurred.The water droplets had a mean diameter of about 0.04 to 0.05 microns,and 94.8% of the water vapor had been recovered from the supersonic gasstream as liquid droplets. The gas stream exiting the de Laval nozzlecontained about 104 ppm water vapor.

Example 7. Drying of an Ethene Stream Containing 0.2%. Water (InitialPressure: 60 Bar)

An ethene gas stream containing 2000 ppm (0.2%) water vapor was modeled,with a starting pressure of 870 psig [60 bar (g)] and a startingtemperature of 305.4° K. The gas stream was tested in a bench-scale deLaval nozzle capable of a ˜Mach 2 expansion.

The ethene gas exiting the de Laval nozzle was substantially dry. Nearcomplete nucleation of the water to form a liquid phase had occurred.The water droplets had a mean diameter of about 0.06 microns, and 94.8%of the water vapor had been recovered from the supersonic gas stream asliquid droplets. The gas stream exiting the de Laval nozzle containedabout 104 ppm water vapor.

Significant nucleation of liquid ethene was observed, as well asnucleation of liquid water. At the throat of the nozzle, a first definedvolume fraction of the gas stream is made up by liquid water (about8.2×10′ liquid water volume/total volume); and a second defined volumefraction of the gas stream is made up by liquid ethene (about 1.3×10′liquid ethene volume/total volume). As the ethene stream expands, thepercentage of water and ethene in the liquid phase decreases. At thenozzle exit, the first liquid water defined volume is about 4.2×10⁻⁵;and the second liquid ethene defined volume is between about 7×10⁻³ and1×10⁻².

Example 8. Drying of a Mixed Hydrocarbon Stream Containing 0.4% Water(Initial Pressure: 31.7 Bar)

A hydrocarbon gas stream containing 4000 ppm (0.4 mol %) water vapor wasmodeled, with a starting pressure of 460 psig [31.7 bar (g)] and astarting temperature of 308.7° K. Based on the total mass of thehydrocarbon gases, the gas stream contained:

-   -   0.9 wt. % methane;    -   67 wt. % ethane;    -   31 wt. % propane;    -   0.3 wt. % n-butane; and    -   0.8 wt. % isobutene.

The gas stream was dried in a bench-scale de Laval nozzle capable of a˜Mach 2 expansion.

Under these conditions, there was near complete condensation of watervapor, with a dry hydrocarbon gas stream exiting the nozzle. Only atrace of the hydrocarbon compounds in the gas stream condensed in thenozzle. The water vapor concentration along the centerline of the deLaval nozzle, measured in ppm, is plotted in FIG. 8 as a function ofdistance, where the nozzle throat is 0.15 m from the nozzle entrance. Asshown in FIG. 8, the water vapor concentration in the gas stream exitingthe nozzle throat is less than 10 ppm.

Example 9. Propene Recovery from a Hydrocarbon Stream ContainingButyraldehydes (Initial Pressure: 31.7 Bar)

A simulated process purge stream was modeled in a de Laval nozzle, wherethe process stream was a hydroformylation purge stream. The purge streamcontained the following molar composition:

-   -   propane 20%,    -   propene 58%,    -   hydrogen 8%,    -   carbon monoxide 3%,    -   argon 1%,    -   methane 3%, and    -   n-butyraldehyde 4%.

The stream was evaluated in the supersonic separator model, with aninitial pressure of 305 psig [21 bar (g)] and 313° K with a flow rate of40 thousand standard cubic feet per minute. Both C3 hydrocarbons(propane and propene) and butyraldehyde were recovered in the condensedliquid phase, with a total C3 hydrocarbon recovery of 24% and a totalbutyraldehyde of 99.8%. The C3 liquid phase was therefore contaminatedwith butyraldehyde, and had a purity of ˜71%. Thus, it is difficult toprepare a pure C3 hydrocarbon phase by condensation in a de Laval nozzlein the presence of a high-boiling condensable vapor, such asbutyraldehyde (boiling point: 348° K). In such a situation, therecovered C3 hydrocarbons may be separated from high-boiling material inthe liquid phase by distillation after supersonic separation in the deLaval nozzle. Alternatively, the high-boiling contaminants can becondensed from the hydroformylation purge stream prior to supersonicseparation.

Although the various exemplary embodiments have been described in detailwith particular reference to certain exemplary aspects thereof, itshould be understood that the invention is capable of other embodimentsand its details are capable of modifications in various obviousrespects. As is readily apparent to those skilled in the art, variationsand modifications can be affected while remaining within the spirit andscope of the invention. Accordingly, the foregoing disclosure,description, and figures are for illustrative purposes only and do notin any way limit the invention, which is defined only by the claims.

What is claimed is: 1-31. (canceled)
 32. A method of drying a vaporstream comprising CI to C4 hydrocarbon gases, or a mixture thereof; saidmethod comprising: passing said vapor stream comprising said CI to C4hydrocarbon gases into an inlet of a de Laval nozzle having a throat,said vapor stream having an initial temperature of between 25° C. and90° C. and an initial pressure of between 150 psig and 1000 psig,wherein the vapor stream contains 500 to 10,000 ppm H₂O by volume;expanding the vapor stream after the vapor stream passes through thethroat of the de Laval nozzle, producing a reduced-temperature vaporstream; condensing said H₂O from the reduced-temperature vapor stream toproduce a dried stream; recovering the condensed H₂O from said vaporstream; and wherein the dried stream comprises said CI to C4 hydrocarbongases and from 0 ppm to 150 ppm water.
 33. The method of claim 32,wherein said vapor stream has an initial temperature of between 25° C.and 40° C.
 34. The method of claim 32, wherein the CI to C4 hydrocarbongases are selected from the group consisting of ethane, ethene, propane,propene, n-butane, isobutane, 1-butene, 2-butene, isobutylene,butadiene, and mixtures thereof.
 35. The method of claim 32, wherein theCI to C4 hydrocarbon gases are C3 gases selected from the groupconsisting of propane, propene, and mixtures thereof.
 36. The method ofclaim 32, wherein the CI to C4 hydrocarbon gases are C2 gases selectedfrom the group consisting of ethane, ethene, acetylene, and mixturesthereof.
 37. The method of claim 32, wherein the CI to C4 hydrocarbongases comprise from 80 to 100% by mass of a mixture of C2 and C3 gases.38. The method of claim 32, wherein the CI to C4 hydrocarbon gasescomprise from 80 to 100% by mass of a mixture of C2 and C3 gases, in aC2 to C3 ratio of between 1:9 and 9:1.
 39. The method of claim 32,further comprising a step of inducing swirling flow in said vapor streamprior to said recovering; wherein said swirling flow drives saidcondensed H₂O toward the wall of said de Laval nozzle or the wall of apipe connected to an exit of said de Laval nozzle by centrifugal force.40. The method of claim 32, wherein the vapor stream comprisescondensable C2 to C4 hydrocarbon gases.
 41. A method of recovering C2 toC4 hydrocarbon gases from a vapor stream comprising C2 to C4 hydrocarbongases; said method comprising: drying said vapor stream comprising C2 toC4 hydrocarbon gases by the method of claim 8 to produce said driedstream; passing said dried stream into an inlet of a de Laval nozzlehaving a throat, said dried stream having an initial temperature ofbetween 0° C. and 100° C. and an initial pressure of between 200 psigand 500 psig; expanding the dried stream after the vapor stream passesthrough the throat of the de Laval nozzle, producing a secondreduced-temperature stream; condensing C2 to C4 hydrocarbons from thesecond reduced-temperature stream as a liquid; and recovering thecondensed liquid C2 to C4 hydrocarbons from said reduced-temperaturestream.
 42. A method of recovering hydrocarbon gases in a vapor streamcomprising C2 to C4 hydrocarbon gases, wherein the vapor stream is awaste gas stream from a chemical reactor, said method comprising: dryingsaid vapor stream comprising C2 to C4 hydrocarbon gases by the method ofclaim 8 to produce said dried stream; passing said dried stream into aninlet of a de Laval nozzle having a throat, said dried stream having aninitial temperature of between 0° C. and 100° C. and an initial pressureof between 200 psig and 500 psig; expanding the dried stream after thevapor stream passes through the throat of the de Laval nozzle, producinga second reduced-temperature stream; condensing C2 to C4 hydrocarbonsfrom the second reduced-temperature stream as a liquid; and at least oneof recycling at least a portion of the condensed C2 to C4 hydrocarbonsto said chemical reactor; or transferring at least a portion of thecondensed C2 to C4 hydrocarbons to a recovery unit.
 43. The method ofclaim 42, wherein the chemical reactor is a hydroformylation reactor.44. The method of claim 42, wherein the chemical reactor is a gas phasepolymerization reactor.
 45. The method of claim 42, wherein the recoveryunit is a propane/propene separator, de-methanizer, or de-propanizer.46. A method of reducing the moisture content of a vapor stream with adefined relative humidity, said vapor stream comprising CI to C4hydrocarbon gases and H₂O, said method comprising: passing said vaporstream at subsonic velocity into an inlet of a de Laval nozzle assembly,said vapor stream having an initial temperature of between 25° C. and90° C. and an initial pressure of between 150 psig and 1000 psig;producing at least one reduced-temperature vapor stream in the de Lavalnozzle assembly; condensing said H₂O from said at least onereduced-temperature vapor stream to produce a dried stream; andrecovering the condensed H₂O; wherein said relative humidity of thevapor stream prior to entering the de Laval nozzle is between about 2%and about 100%; and wherein the dried stream comprises said CI to C4hydrocarbon gases and from 0 ppm to 150 ppm water.
 47. The method ofclaim 46, wherein the de Laval nozzle assembly comprises at least two deLaval nozzles connected in series; wherein said producing at least onereduced-temperature vapor stream comprises: accelerating said vaporstream to supersonic velocity in a first de Laval nozzle to produce afirst reduced-temperature vapor stream; passing the vapor stream from anoutlet of said first de Laval nozzle to an inlet of a second de Lavalnozzle; and accelerating said vapor stream to supersonic velocity in thesecond de Laval nozzle to produce a second reduced-temperature vaporstream.
 48. The method of claim 47, wherein said recovering thecondensed H₂O comprises recovering the condensed H₂O from said firstreduced-temperature vapor stream and from said secondreduced-temperature vapor stream.
 49. The method of claim 47, whereinthe de Laval nozzle assembly comprises at least two de Laval nozzlesconnected in parallel.
 50. The method of claim 47, wherein the de Lavalnozzle assembly comprises: a) a low-temperature condenser whichcondenses a portion of said H₂O from said vapor stream at subsonicvelocity; connected in series with b) a de Laval nozzle whichaccelerates said vapor stream to supersonic velocity to produce said c)reduced-temperature vapor stream.